The extracellular Glucans of Streptococcus mutans are involved both in the adhesive interactions among these organisms and in their colonization of the tooth surface. The mechanisms by which these polysaccharides are synthesized and the nature of their chemical structure, therefore, are being actively studied. The constitutive extra-cellular glucan synthesizing system (Glucosyltransferases) of S. mutans 6715 has been extensively purified. The purified system has been resolved into two major enzyme components (making either water soluble or insoluble products), each of which contains several catalyzically active glycoprotein species. The interaction of these enzyme species in glucan formation and their glycoprotein nature are under investigation. Various inhibitors of glucan formation are being sought as an approach to the effective prevention of microbial colonization of the tooth surface. The feasibility of using purified glucosyltransferase preparations in a vaccine against dental caries is also being studied. The enzyme systems of the five different Bratthall serotypes of S. mutans have been characterized and compared both immunologically and biochemically. Studies in animal models are now in progress.